Thousands of documents from across Whitehall have been declassified and prepared for publication alongside a final report which will run to more than one million words.

Mr Brown set up the inquiry into the war under Sir John Chilcot, a former civil servant, when he was Prime Minister in June 2009.

It was in November disclosed that the Cabinet Office was resisting requests to make public “more than 130 records of conversations” between either Mr Brown or Tony Blair, his predecessor, and Mr Bush, the former US president, Sir John said in a letter.

There was also a wrangle about making public “25 Notes from Mr Blair to President Bush and “some 200 Cabinet-level discussions”, he said.

According to reports Sir Jeremy Heywood, the Cabinet Secretary, now wants to release as many of the papers as possible.

If the documents are published, some of their contents will be blacked out for national security reasons.

A spokesman for Mr Blair told the Mail: "The inquiry of course had full access to all documents, including all the confidential correspondence between president Bush and then prime minister, Mr Blair.

"In addition, Mr Blair agreed at the last inquiry hearing to answer questions in a way that specifically revealed the contents of the correspondence on the issues that interested the inquiry."

A Cabinet Office spokesman said: "The Government is currently engaged in discussions with the inquiry, which the inquiry recognises raises difficult issues, including legal and international relations issues.

"These issues are being worked through in good faith and with a view to reaching a position as rapidly as possible.

"The inquiry should be allowed to publish its findings and we should not pre-empt the content of the report."